将BigDecimal转换为double值

Question

I want to ask how to transform all my String to double with exponential. when I use the string that length is over seven it's doing fine .

new BigDecimal("12345678").doubleValue() => 1.2345678E7

but seven and under I can't export exponential number.

new BigDecimal("1234567").doubleValue() => 1234567.0

what I want is like 1.234567E6.

Is there any way to do this? I've been searching for a while ,but got nothing.

The problem is the type I return must be double . After transforming the value under seven I can only get the value without exponential.

double test = new BigDecimal("1.234567E6").doubleValue() ;//output 1234567.0 

but I need it to be 1.234567E6 and return to caller. Is that Impossible?

Answer 1

For your problem, you want to convert the value to the BigDecimal with exponential, you can use the DecimalFormat . You can also change the scale for the output value digits.

import java.math.*;
import java.text.*;
public class HelloWorld{

     public static void main(String []args){
        double a = new BigDecimal("1234567").doubleValue();
        String b;
        System.out.println(a);

        NumberFormat formatter = new DecimalFormat("0.0E0");
        formatter.setRoundingMode(RoundingMode.DOWN);
        formatter.setMinimumFractionDigits(5); //<---Scale
        b = formatter.format(a);

        System.out.println(b);
     }
}

The output will be like:

1234567.0 //Unformatted Value
1.23456E6 //Formatted Value

Answer 2

You should know that 1.2345678e7 and 12345678.0 are exactly the same value, only with different textual representations . You could represent 1234567.0 as 1.234567e6 too. Also exactly the same double, just a different way of writing it out.

The default output shows values with more than a certain number of significant digits in exponential format ("e-form"), otherwise as plain decimal format.

So you may want to change the formatting of the doubles you receive. This can be done with eg DecimalFormat or String.format() or similar. That does not change the doubles, only the way they are presented in a string.

Answer 3

See the section about Scientific Notation in java.text.DecimalFormat .

For example,

    DecimalFormat scientificFormat = new DecimalFormat("0.###E0");
    System.out.println(scientificFormat.format(BigDecimal.valueOf(123456L)));
    System.out.println(scientificFormat.format(BigDecimal.valueOf(1234567L)));

    scientificFormat.setMinimumFractionDigits(10);
    System.out.println(scientificFormat.format(BigDecimal.valueOf(12345678L)));

would give you

1,235E5
1,235E6
1,2345678000E7

Change the pattern to match what you're looking for.